Is swearing falsely by Allah and by one’s mother’s life to protect a friend from bad company considered haram (forbidden), and how can one expiate this sin, and does harm befall the mother from swearing falsely by her life?

The inquirer is not considered a liar in his oath, nor is there any sin upon him, because his friend has repented from sins, and one who repents is like one who has no sin. As for swearing by the life of one's mother, its expiation is the saying: "There is no god but Allah." It is absolutely forbidden, whether one is truthful or a liar, because swearing by other than Allah is forbidden.